void main(List<String> args) {
  //字典
  Map<String,int> scores = {'张三':90,'李四':80,'王五':70};
  print(scores);
  //访问元素
  print(scores['张三']);
  //添加元素
  scores['赵六'] = 60;
  print(scores);
  //删除元素
  scores.remove('王五');
  print(scores);
  //遍历元素
  scores.forEach((key, value) {
    print('$key:$value');
  });
}